甘肃龙首山新元古代烧火筒群沉积特征及其构造意义

华北地块西南缘龙首山隆起广布一套前寒武纪碳酸盐质为主要成分组成的碎屑流沉积,近年来发现在邻区北山、祁连山地区亦有分布。岩石状貌特殊,砾石大小混杂,呈无磨圆的棱角、半棱角状,为杂基支撑结构。区域上岩层连续性好,但厚薄不一,厚几米至几十米,局部与火山岩相变。根据其上覆、下伏岩层同位素年龄和微古植物化石定年资料,分析判断为新元古代中晚期的产物,讨论其成因为大陆裂谷沉积构造环境下,地壳急剧动荡,崩塌原稳定台地相的沉积,大量崩塌堆积物在大陆裂谷斜坡形成碎屑流移动而成。其为大陆裂谷的典型沉积,具有重要的指相意义。龙首山及邻区新元古代中晚期大面积碎屑流沉积分布,表证当时大规模大陆裂谷作用的发生,与全球性Rodinia大陆裂解的认识一致.

Late Neoproterozoic Sedimentations of the Carbonate-Detrital Flows in Longshou Mountains, Northwest China:Implications for Its Tectonic Environments

In Longshou Mountains of the southwestern margins of North China's Plate, there is extensively a series of Pre Cambrian sedimentary of the detrital flows consisting of dominant carbonate, and the sedimentary rocks have also been found in recent years. The rocks are characterized by chaotic gravels on grain sizes, dominant dolomite gravels, bed rounded gravels showing angulate subangulate, and textures of matrix support. In the region the sediments distributed continuously, but its thickness is various from several meters to tens of meters, locally transforming to volcanic rocks. On the basis of the isotopic ages and micro paleobotanic fossils of the over and underlain strata, the sedimentary rocks were suggested forming in late Neoproterozoic era. Its origin is thought to be the sediments of the carbonate -fragmental flows, on a sedimentary-tectonic environment of paleo-continental rift, coming from large quantities of collapse files on slope of continental rift due to crustal movement rapidly to lead to breakdown of sedimentary rocks on steady platform. So these rocks are the typical sediments of the continental rift, and important significance on implication for the tectonic environments. In Longshou Mountains and neighboring area the distribution of large quantities of the late Neoprozoic sediments of palaeo-fargmental flows indicate that in that time a large scale of continental rift had occurred and consistent with splitting recognition of the Rodinia continent globally.